Infiniti G37 Coupe Zenclosures Sealed Box

Should I use stuffing in this sealed box for two 10" speakers with 0.5 cu ft chambers? I'm using Dayton Audio RSS265HO-44 10" subs wired for 4 ohms and a Zapco ST-1650XM ll mono amp. I've got stuffing in there at present but I just can't seem to get it to sound right. Very strong low bass and very weak mid and upper bass. I was hesitant to put stuffing in there to start with as the chambers are so small and now I'm wondering if I did the right thing. I'm limited as to what box I can use in the G37 as the trunk is very small. The Dayton's specs say they'll work in this small 0.5 cu ft space. Where should I go from here? It just sounds pretty much like a one note wonder at present.